1. Field of the Invention
The present invention relates to a piezoelectric transformer using a piezoelectric ceramics as an element for generating high voltage, and as an element for converting voltage.
2. Description of the Related Art
A piezoelectric transformer using a piezoelectric ceramics is widely used for a light source for a backlight which illuminates from a rear side a liquid crystal used in a personal computer and the like, used for a DC/DC converter of a power supply, and for a high-voltage power source of an air cleaner and the like. This kind of piezoelectric transformer is obtained by providing primary and secondary electrodes to a piezoelectric ceramics such as PZT, and polarizing it by applying a high electric field to the respective electrodes to align crystal axes.
Conventionally, in a general piezoelectric transformer, as shown in FIG. 6, primary side electrodes 3′ are provided by printing on the top and bottom surfaces of one half of an elongated piezoelectric ceramics 2′ having a rectangular shape viewed from the upper side, and secondary side electrodes 4′ having a rectangular shape are similarly provided by printing at the outer ends of the top and bottom surfaces in the other half.
In this piezoelectric ceramics 2′, a generating part between the primary side electrodes 3′ is polarized, for example, in a direction shown by an arrow a, and an output part side at the other half part is polarized, for example, in a direction shown by an arrow b. A piezoelectric transformer 1′ is configured by such polarizations.
In the piezoelectric transformer 1′, when a voltage with a unique resonant frequency decided by a longitudinal direction of the primary side of the transformer is applied, elements are vibrated by counter-piezoelectric effect, and a positive or negative voltage corresponding to the vibrations can be picked up from the secondary side by piezoelectric effect. The characteristics of the transformer can be changed by changing a polarization direction.